Other Factors Affecting
Nitrogen Fixation

Rhizobia bacteria
require the availability of molybdenum (Mo), a soil element. In Pennsylvania,
Mo is generally present in soils in sufficient quantity, but its availability
is affected greatly by the soil pH. Soil into which a legume is being
planted should be limed to raise the pH to between 6.5 and 7.0.

Some inoculants or
preinoculated seed maybe sold with combinations of Mo and or a fungicide.
These additional treatments tend to reduce the number of live Rhizobia
and generally are not recommended.

When establishing
forage legumes, 20 pounds of nitrogen per acre is often recommended as
a starter application. However, if conditions at planting are favorable
for quick seed germination and seed has been inoculated, this starter
nitrogen fertilizer is often unnecessary.

Do not apply nitrogen
fertilizer to established legumes. Legumes can fix all the nitrogen they
need for growth. Research has shown that nitrogen fertilizer does not
increase yield of established legumes if the plants are effectively nodulated.
In fact, fertilizer nitrogen discourages nodulation and inhibits nitrogen
fixation.